(CNSNews.com) - Australian Muslims already unhappy with Prime Minister John Howard's criticism about Islamic radicalism are bristling at even tougher comments from the man likely to succeed him, who says any Muslim immigrant who can't accept Australian values should leave.

Anyone wanting to live under Islamic law (shari'a) might feel more comfortable living in countries where it is applied, such as Saudi Arabia or Iran, federal Treasurer Peter Costello said in an address to the Sydney Institute, a think tank.

In a pledge of allegiance, immigrants taking on Australian citizenship declare: "I pledge my loyalty to Australia and its people, whose democratic beliefs I share, whose rights and liberties I respect and whose laws I will uphold and obey."

Costello said that anyone "who does not acknowledge the supremacy of civil law laid down by democratic processes cannot truthfully take the pledge of allegiance. As such they do not meet the pre-condition for citizenship."

Any Muslim planning to immigrate to Australia should first consider its values.

"Before entering a mosque visitors are asked to take off their shoes," Costello said. "This is a sign of respect. If you have a strong objection to walking in your socks don't enter the mosque.

"Before becoming an Australian you will be asked to subscribe to certain values. If you have strong objection to those values, don't come to Australia."

The debate in Australia over Islam and its more radical adherents has been picking up steadily since 9/11, becoming more urgent after 88 Australians were killed when Islamists bombed an Indonesian tourist resort in 2002, and focusing increasingly on homegrown extremists after last July's London bombings, carried out by British-born Muslims.

Costello, who is widely expected to take over the leadership of Howard's conservative Liberal party within the next couple of years, said anyone applying for citizenship who rejects the notion of living under a democratic legislature and obeying the laws it makes, poses a threat to the rights and liberties of others, and should be refused citizenship.

If foreign-born Muslims who have already become Australian citizens, having not been able honestly to take the citizenship pledge, they should be stripped of their Australian nationality if they also have citizenship of some other country.

In cases where Muslims were born in Australia and did not have dual citizenship, there was a difficulty.

"In these cases we have on our hands citizens who are apparently so alienated that they do not support what their own country stands for. Such alienation could become a threat to the rights and liberties of others."

Costello said for such Muslims it was important that the government engage respected leaders for help in explaining Australian values.

"Ultimately, however, it is important that they know that there is only one law and it is going to be enforced whether they acknowledge its legitimacy or not."

Costello also made a point of saying that among Australian values were tolerance of difference and the protection of the rights and liberties of all.

While he did not like artworks mocking Christianity, galleries that displayed them "should be able to practice their offensive taste without fear of violence or a riot."

Muslims, too, must recognize that their opposition to newspapers publishing pictures depicting Mohammed does not justify violence.

'Raving about jihad'

Costello's comments come amid a debate over earlier ones by Howard, who criticized a radical minority of Muslims whom he said "rave on about jihad" and hold "extreme attitudes" towards women.

Six million migrants have made Australia home since World War II -- a number comprising almost one-third of the country's current population. But Howard said Australia had never before had to deal with newcomers bent on overturning its core beliefs and values.

"It is not a problem that we've ever faced with other immigrant communities, who become easily absorbed by Australia's mainstream."

Publication of the comments this week provoked outrage from Muslim representatives, who called them "offensive and ignorant" and said they were feeding "Islamophobia."

Similar reaction met Costello's speech.

Muslims comprise only around 300,000 of Australia's 20 million people, although in the five years leading up to a census in 2001, the Muslim population increased by 40 percent, compared to growth of 5.7 percent of the Australian population as a whole, according to government statistics.

As in other Western countries, most Muslims are considered moderate, but vocal clerics emerge from time to time to espouse extremist views.

Twenty-four Muslims have been prosecuted under anti-terrorism laws introduced since 9/11. Only one has been convicted to date, a British-born convert to Islam jailed for nine years for plotting with al-Qaeda to bomb Israel's embassy in Canberra.

Mainstream Muslim organizations speak out against terror, while condemning the policies which the governments of Australia, the U.S. and other allies say are aimed at combating terrorism.

Spokesmen also claim that Australia's military role in Iraq and Afghanistan and its support for Israel are fueling radical sentiment among Australian Muslims.